diff --git a/chrome/content/zotero/xpcom/pdfWorker/manager.js b/chrome/content/zotero/xpcom/pdfWorker/manager.js
index 520044f1b2..8a911c0558 100644
--- a/chrome/content/zotero/xpcom/pdfWorker/manager.js
+++ b/chrome/content/zotero/xpcom/pdfWorker/manager.js
@@ -242,23 +242,24 @@ class PDFWorker {
 					annotation.key = Zotero.DataObjectUtilities.generateKey();
 					await Zotero.Annotations.saveFromJSON(attachment, annotation);
 				}
-				Zotero.PDF.hasUnmachedAnnotations[itemID] = false;
+				attachment.attachmentHasUnimportedAnnotations = false;
 			}
 			else {
-				Zotero.PDF.hasUnmachedAnnotations[itemID] = !!annotations.length;
+				attachment.attachmentHasUnimportedAnnotations = !!annotations.length;
 			}
 			for (let reader of Zotero.Reader._readers) {
 				if (reader._itemID === itemID) {
-					reader.toggleImportPrompt(!!Zotero.PDF.hasUnmachedAnnotations[itemID]);
+					reader.toggleImportPrompt(attachment.attachmentHasUnimportedAnnotations);
 				}
 			}
-			Zotero.PDF.dateChecked[itemID] = Zotero.Date.dateToISO(new Date());
+			attachment.attachmentLastProcessedModificationTime = await attachment.attachmentModificationTime;
+			await attachment.saveTx();
 			return annotations.length;
 		});
 	}
 	
 	/**
-	 * Import children PDF attachment annotations
+	 * Import annotations for each PDF attachment of parent item
 	 *
 	 * @param {Zotero.Item} item
 	 */
diff --git a/chrome/content/zotero/xpcom/reader.js b/chrome/content/zotero/xpcom/reader.js
index fce4018413..83c192c579 100644
--- a/chrome/content/zotero/xpcom/reader.js
+++ b/chrome/content/zotero/xpcom/reader.js
@@ -46,7 +46,7 @@ class ReaderInstance {
 			annotations,
 			state,
 			location,
-			promptImport: !!Zotero.PDF.hasUnmachedAnnotations[this._itemID],
+			promptImport: item.attachmentHasUnimportedAnnotations,
 			showItemPaneToggle: this._showItemPaneToggle,
 			sidebarWidth: this._sidebarWidth,
 			sidebarOpen: this._sidebarOpen,
@@ -811,8 +811,7 @@ class Reader {
 	async triggerAnnotationsImportCheck(itemID) {
 		let item = await Zotero.Items.getAsync(itemID);
 		let mtime = await item.attachmentModificationTime;
-		let dateModified = Zotero.Date.dateToISO(new Date(mtime));
-		if (!Zotero.PDF.dateChecked[itemID] || Zotero.PDF.dateChecked[itemID] < dateModified) {
+		if (item.attachmentLastProcessedModificationTime < mtime) {
 			await Zotero.PDFWorker.import(itemID, false);
 		}
 	}